Read the comments on phoronix, it looks like there are different 9400 steppings and the one tested didn't have the h/w mitigations.
I was expecting that hardware mitigation would give better performance but Intel did a disappointing job.
I request that mods do not change this title,
Intel Core i5 8400 vs. i5 9400F means very little to anyone without good knowledge of difference between Intel CPU generations.
The new 9xxx series CPUs have mitigations baked into the CPU hardware out of the box, vs the 8xxx series which do not.